The invention relates to the field of scanning tip and electron beam lithography, and in particular nanometer-level mix-and-match scanning tip and electron beam lithography using global backside position reference marks.
Previous forms of infrared alignment used conventional alignment marks, such as crosses and boxes, and were imaged with conventional optics. Resolution using conventional imaging techniques is limited to approximately λ/2. To view backside alignment marks, infrared illumination is required. At the longer, infrared wavelengths, resolution degrades, typically to 500 nm or more. In a special case, signal processing was applied to such low-resolution images to improve resolution in a 1000 nm-resolution infrared imaging system, signal processing techniques extended matching precision of a known pattern to infrared images within ˜100 nm, which is still insufficient for many applications.
Moreover, U.S. Pat. No. 5,136,169 describes the use of fiducial patterns written on a layer on top of an e-beam resist, for the purpose of detecting the position of the e-beam relative to the substrate, and correcting e-beam position drift. U.S. Pat. No. 6,882,477 describes a method for nanometer-precision formation of periodic patterns, for fabrication of large-area periodic structures. U.S. Pat. No. 6,437,347 describes a target-locking system for electron beam lithography, but uses a dual-frequency laser stage interferometer to relate the position of a target plate to a substrate stage, and is unable to relate the position of e-beam-written patterns to patterns written by a scanning tip.